Fix submitting attachments with 'bk sendbug' in Windows. Also add a 'file select' button to the attachment field so that users don't have to type the pathname. 
Fix submitting attachments with 'bk sendbug' in Windows.
Also add a 'file select' button to the attachment field so
that users don't have to type the pathname. 

The bug was that we were passing a string with backslashes to 
the shell as the attachment path. If the user typed forward
slashes instead of backslashes, then it worked (but who would
think of this on Windows?).

bk: 43286492vq0_XdSaOt6-97cxNj5bdg
bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper